Synthetic polymers have a wide variety of commercial applications. For example, synthetic polymers are used in the production of polymer end products such as plastics, films, fibers, adhesives, paints, and the like.
Conventional polymerization processes produce synthetic polymers containing impurities such as, by-products, unreacted monomers, oligomers, catalysts, chain-length control agents, and the like. Such polymer impurities often impair or damage the machinery used to process the polymer. In addition, as the polymer is processed, impurities in a polymer act as a source of pollution and thus a safety hazard to those operating the processing machinery. Furthermore such impurities adversely effect the properties of the polymer and, as a result, the properties of the polymer end products. For example, the presence of unreacted monomers can cause the polymer to be sticky or weak and consequently creates problems when processing the polymer into films or fibers. Accordingly, in order to optimize the properties of the polymer end products, it is desirable to use a synthetic polymer that contains no impurities or as few impurities as possible.
The removal of impurities remaining after polymerization from a synthesized polymer is generally achieved by washing or extracting the polymer with a solvent, such as water. For example, U.S. Pat. Nos. 3,245,964 and 3,373,145 describe processes for extracting water-soluble impurities from polymer chips or pellets by washing the polymer chips or pellets with water. The resulting leachate, i.e., the leaching solvent now containing the impurity, is then removed from the polymer. However, such leaching processes require continuous and prolonged contact (e.g., more than 20 hours per polymer batch) of the leaching solvent, in this case water, with the polymer to achieve sufficient removal of impurities. Such treatments are not only time consuming and costly but inconsistent, frequently leading to variations among the polymer batches obtained. Moreover, prolonged exposure of the polymer to the aqueous leaching solvent can lead to deterioration of the polymer. Consequently, the appearance of the polymer and/or the mechanical properties of the polymer and polymer end products are adversely effected.
Ultrasound has been used for the removal of residual monomer from oriented polymer fibres formed from a precursor polymer. P. Greguss et al., Acoustic Method for the Post-treatment of Fibres, 1st International Symposium High Power Ultrasonics, p. 154 (1966). According to such a method, ultrasound is applied after fibre formation to remove any residual monomer content. Thus, the method is used as a post-treatment method of processed oriented polymers.
Accordingly, there still exists a need in the art for an effective and efficient method for the removal of impurities present in substantially unoriented polymers. The invention answers this need.